Choose Windows->Show Channels Click the fourth channel to bring up the alpha channel, you may want to modify it.Click the first RGB channel to bring you back to the main image.You may save as many alpha selection channels as you like.

Layers:Choose Edit->Copy (This saves the selected area to a temporary buffer.)

Choose Edit->Paste (Paste the selection into a new layer.)

Choose Windows->Show Layers (Layers is a tab under the Channels tab.)

You can select separate layers to modify.Notice the top layer has transparency or alpha, this is another alpha channel.

Select the Background Layer from the Layers window.Choose Select->AllHit the Delete Key on the keyboard.Notice the image fills with the background color in the Tools window.

Select a new color, please notice how this effects the feeling or your perception of the image.

Click the small arrow on the upper right of the Layers window to bring up the menuChoose Flatten image This will merge the two layers.You lose the alpha information from the layer.You still have the alpha information in the Channels window.If you do not understand the difference ask!